COFFEEMUD  [codebase]
A MUD server in Java, with the largest MSSP report of anything we have probed
and an unusually broad protocol surface.
https://www.coffeemud.net/

Games we have identified as running this codebase
  32 listed, 0 archived
  /games?codebase=CoffeeMUD
  Measured in their handshakes: MCCP, MXP, MSSP, MSDP

CoffeeMUD is a Java MUD server with an unusually wide feature surface — it ships
with its own web server, mail, forums and a large class and skill system, and it
is one of the few servers in the hobby not written in C.

It is actively maintained, which by the standards of this part of the catalogue
is worth saying out loud.

WHAT IT LOOKS LIKE FROM OUTSIDE

MSSP and MCCP2, and CoffeeMUD is one of only three servers out of twenty we
tried that also answered the plaintext MSSP-REQUEST form — a variant that
predates the telnet option and is still occasionally seen.

Its MSSP report is the largest we have measured: 47 fields, including PORT
reported nine separate times for nine separate ports. That is not a
malformation. MSSP variables are lists, and a crawler that flattens a
multi-valued PORT into one string produces the integer 80234201 out of "80" "23"
"4201" — which is a bug this project shipped and fixed, and the reason the
parser here keeps values as lists throughout.

See also
  DikuMUD — /reference/codebases/dikumud
  MSSP — /reference/protocols/mssp